Linear power manager

Linear Technology has announced the LTC3577, LTC3577-1, LTC3577-3 and LTC3577-4 integrated multi-function power management integrated circuit solutions for portable Li-Ion/polymer battery applications. They integrate a USB-compatible linear PowerPath manager, a standalone battery charger, overvoltage protection, 10-LED driver, push-button on/off control, three high-efficiency synchronous buck regulators and two LDOs.

The LTC3577-1 and LTC3577-4 feature a 4.1 V battery float voltage for improved battery cycle life and additional high-temperature safety margin, while the LTC3577 and LTC3577-3 include a standard 4.2 V battery float voltage for maximum run time.

The LTC3577-3 and LTC3577-4 are tailored for SiRF Atlas IV chipsets. These ICs are suitable for portable devices including personal navigation devices, digital media/video broadcasting, digital/satellite radio, media players, universal remotes, photo viewers and portable medical and industrial devices.

The devices’ PowerPath manager with automatic load prioritisation manages the transition between multiple input sources to power the load, while delivering up to 1.5 A of battery charge from a wall adapter supply or up to 500 mA charge current from a USB port.

The charger is compatible with inputs up to 5.5 V (7 V absolute maximum transient for added robustness). The ICs ‘instant-on’ operation ensures system load power even with a fully discharged battery.

Autonomous operation simplifies design, eliminating the need for an external microprocessor for charge termination. An overvoltage protection controller enables up to 30 V protection for the wall/USB input, while a high-temperature battery voltage reduction circuit improves battery safety and reliability.

To preserve battery energy during long periods of inactivity or to reset the product in the event of a software lockup, the LTC3577/-1 contains a hard reset function enabled via push-button control, placing the IC into an ultra-low quiescent current state that draws <10 µA and disables all power supplies and power paths.

The LTC3577/-1 can control an external high-voltage buck regulator to achieve high-efficiency Bat-Track charging and power path control from a high-voltage source, reducing power dissipation. The internal 200 mΩ diode, plus an optional external ideal diode controller provide a low loss power path to the load when input current is limited or unavailable.

The devices’ three integrated synchronous buck regulators feature 100% duty cycle operation and are capable of delivering output currents of 800/500/500 mA with adjustable output voltages down to 0.8. A high 2.25 MHz switching frequency allows the use of low-cost capacitors and inductors.

In addition, 1²C-controlled burst mode operation optimises efficiency at light loads with a quiescent current of only 20 µA per regulator (<1 µA in shutdown). The regulators are stable with ceramic output capacitors, achieving low output voltage ripple.

Additional features include a 40 V series backlight 10-LED driver with 1²C controlled 60 dB brightness (1000:1 dimming range) and gradation control, push-button on/off control with system reset and dual 150 mA current limited LDOs.